procfs man page on FreeBSD

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PROCFS(5)		    BSD File Formats Manual		     PROCFS(5)

     procfs — process file system

     proc	     /proc   procfs  rw 0 0

     The process file system, or procfs, implements a view of the system
     process table inside the file system.  It is normally mounted on /proc,
     and is required for the complete operation of programs such as ps(1) and

     The procfs provides a two-level view of process space, unlike the previ‐
     ous FreeBSD 1.1 procfs implementation.  At the highest level, processes
     themselves are named, according to their process ids in decimal, with no
     leading zeros.  There is also a special node called curproc which always
     refers to the process making the lookup request.

     Each node is a directory which contains the following entries:

     Each directory contains several files:

     ctl     a write-only file which supports a variety of control operations.
	     Control commands are written as strings to the ctl file.  The
	     control commands are:
	     attach  stops the target process and arranges for the sending
		     process to become the debug control process.
	     detach  continue execution of the target process and remove it
		     from control by the debug process (which need not be the
		     sending process).
	     run     continue running the target process until a signal is
		     delivered, a breakpoint is hit, or the target process
	     step    single step the target process, with no signal delivery.
	     wait    wait for the target process to come to a steady state
		     ready for debugging.  The target process must be in this
		     state before any of the other commands are allowed.

	     The string can also be the name of a signal, lower case and with‐
	     out the SIG prefix, in which case that signal is delivered to the
	     process (see sigaction(2)).

	     The procctl(8) utility can be used to clear tracepoints in a
	     stuck process.

     dbregs  The debug registers as defined by struct dbregs in
	     <machine/reg.h>.  dbregs is currently only implemented on the
	     i386 architecture.

     etype   The type of the executable referenced by the file entry.

     file    A symbolic link to the file from which the process text was read.
	     This can be used to gain access to the process' symbol table, or
	     to start another copy of the process.  If the file cannot be
	     found, the link target is ‘unknown’.

     fpregs  The floating point registers as defined by struct fpregs in
	     <machine/reg.h>.  fpregs is only implemented on machines which
	     have distinct general purpose and floating point register sets.

     map     A map of the process' virtual memory.

     mem     The complete virtual memory image of the process.	Only those
	     address which exist in the process can be accessed.  Reads and
	     writes to this file modify the process.  Writes to the text seg‐
	     ment remain private to the process.

     note    Used for sending signals to the process.  Not implemented.

     notepg  Used for sending signal to the process group.  Not implemented.

     osrel   Allows read and write of the kernel osrel value assigned to the
	     process.  It affects the compatibility shims that are turned on
	     and off depending on the value.  Initial process value is read
	     from the ABI note tag in the executed ELF image, and is zero if
	     the tag not supported by binary format or was not found.

     regs    Allows read and write access to the process' register set.	 This
	     file contains a binary data structure struct regs defined in
	     <machine/reg.h>.  regs can only be written when the process is

     rlimit  This is a read-only file containing the process current and maxi‐
	     mum limits.  Each line is of the format rlimit current max, with
	     -1 indicating infinity.

     status  The process status.  This file is read-only and returns a single
	     line containing multiple space-separated fields as follows:

	     ·	 command name
	     ·	 process id
	     ·	 parent process id
	     ·	 process group id
	     ·	 session id
	     ·	 major,minor of the controlling terminal, or -1,-1 if there is
		 no controlling terminal.
	     ·	 a list of process flags: ctty if there is a controlling ter‐
		 minal, sldr if the process is a session leader, noflags if
		 neither of the other two flags are set.
	     ·	 the process start time in seconds and microseconds, comma
	     ·	 the user time in seconds and microseconds, comma separated.
	     ·	 the system time in seconds and microseconds, comma separated.
	     ·	 the wait channel message
	     ·	 the process credentials consisting of the effective user id
		 and the list of groups (whose first member is the effective
		 group id) all comma separated.
	     ·	 the hostname of the jail in which the process runs, or ‘-’ to
		 indicate that the process is not running within a jail.

     In a normal debugging environment, where the target is fork/exec'd by the
     debugger, the debugger should fork and the child should stop itself (with
     a self-inflicted SIGSTOP for example).  The parent should issue a wait
     and then an attach command via the appropriate ctl file.  The child
     process will receive a SIGTRAP immediately after the call to exec (see

     Each node is owned by the process's user, and belongs to that user's pri‐
     mary group, except for the mem node, which belongs to the kmem group.

     /proc		    normal mount point for the procfs.
     /proc/pid		    directory containing process information for
			    process pid.
     /proc/curproc	    directory containing process information for the
			    current process
     /proc/curproc/cmdline  the process executable name
     /proc/curproc/ctl	    used to send control messages to the process
     /proc/curproc/etype    executable type
     /proc/curproc/file	    executable image
     /proc/curproc/fpregs   the process floating point register set
     /proc/curproc/map	    virtual memory map of the process
     /proc/curproc/mem	    the complete virtual address space of the process
     /proc/curproc/note	    used for signaling the process
     /proc/curproc/notepg   used for signaling the process group
     /proc/curproc/osrel    the process osrel value
     /proc/curproc/regs	    the process register set
     /proc/curproc/rlimit   the process current and maximum rlimit
     /proc/curproc/status   the process' current status

     To mount a procfs file system on /proc:

	   mount -t procfs proc /proc

     procstat(1), mount(2), sigaction(2), unmount(2), procctl(8), pseudofs(9)

     This manual page written by Garrett Wollman, based on the description
     provided by Jan-Simon Pendry, and revamped later by Mike Pritchard.

BSD			      September 22, 2009			   BSD

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